1. Field of the Invention
The present invention relates generally to a method and base station for allocating a DownLink (DL) Hybrid Automatic Repeat Request (HARQ) channel in a wireless communication system, and more particularly, to a method and base station for allocating a DL HARQ channel according to service flow types.
2. Description of the Related Art
A HARQ operation of a DL in a wireless communication system is provided in detail below.
The HARQ technique in a wireless communication system is used to reduce influences of a channel and interference fluctuation. By using the HARQ technique, a Signal to Noise Ratio (SNR) can be increased and a time diversity effect can be obtained, thereby enhancing communication performance.
When a base station transmits a HARQ burst to a mobile station, it also transmits a HARQ Channel Identifier (ACID) indicating a HARQ channel through which the HARQ burst is transmitted and a HARQ identifier Sequence Number (AI_SN) indicating whether current transmission of the HARQ burst is an initial transmission or a retransmission to the mobile station, together with the HARQ burst.
If there is no error in the HARQ burst that is received by the mobile station, the mobile station transmits an ACKnowledgement (ACK) to the base station. Upon receiving the ACK for the corresponding ACID from the mobile station, the base station transmits an initial HARQ burst containing new data to the mobile station through the HARQ channel indicated by the ACID.
If an error occurs in the received HARQ burst, the mobile station transmits a Non-ACKnowledgement (NACK) to the base station. Upon receiving the NACK for the corresponding ACID, the base station retransmits the HARQ burst to the mobile station through the HARQ channel indicated by the ACID. Upon receiving the retransmitted HARQ burst, the mobile station combines the HARQ burst transmitted previously through the HARQ channel indicated by the ACID with the retransmitted HARQ burst and decodes the combination.
FIG. 1 is a diagram illustrating a wireless communication system in which a mobile station is provided with one or more service flows from a base station.
A mobile station 102 may be provided with data of one or more Service Flows (SFs) from a base station 100. Thus, the data of several SFs related to the mobile station 102 may be contained in one HARQ burst. For example, a HARQ burst transmitted from the base station 100 to the mobile station 102 may contain data of a delay tolerant SF, such as a Best Effort (BE) service, and data of a delay intolerant SF, such as a Voice over Internet Protocol (VoIP) service.
As such, when both the data of the delay tolerant SF and the data of the delay intolerant SF are contained in the single HARQ burst, if the delay tolerant SF, which occupies a greater amount of traffic than the VoIP SF, uses all HARQ channels, the delay intolerant SF may not be allocated resources at once.
Hence, in an IEEE 802.16e system, a HARQ channel for a particular SF may be designated (or reserved) through a HARQ channel mapping Type/Length/Value (TLV) field, which is one of a plurality of Information Elements (IEs) transmitted from a base station to a mobile station. Specifically, the HARQ channel for the VoIP SF is separately designated (or reserved), such that the designated (or reserved) HARQ channel cannot be used by other SFs.
Moreover, in the IEEE 802.16e system, after a particular SF is connected between a mobile station and a base station, the base station cannot dynamically change an already allocated HARQ channel by using a HARQ channel mapping TLV field. Therefore, even if a VoIP SF is not currently connected, a HARQ channel has to be reserved in advance for the VoIP SF that may be connected later.
As a result, if a HARQ channel for a particular SF has been reserved through a HARQ channel mapping TLV field, a single user peak throughput that a single SF can obtain is lower than when a HARQ channel is not reserved. This result is due to the fact that the number of HARQ channels the single SF can use is reduced by the number of reserved HARQ channels.